Low standby power with fast turn on method for non-volatile memory devices

ABSTRACT

A method for driving a non-volatile memory system is disclosed. A standby detection circuit detects whether the nonvolatile memory system is in a standby condition. In response to determining that the non-volatile memory system is in a standby condition, a bias control circuit reduces bias currents provided to drivers of the non-volatile memory system in a standby mode. The non-volatile memory system is operated in the standby mode after the bias currents have been reduced, where an output signal indicating the standby mode is maintained until a read instruction is detected.

RELATED APPLICATIONS

This Application is a Continuation of U.S. patent application Ser. No.15/268,315, filed on Sep. 16, 2016, which is a Continuation of U.S.patent application Ser. No. 14/966,990, filed on Dec. 11, 2015, now U.S.Pat. No. 9,449,655, which issued on Sep. 20, 2016, which claims thebenefit of U.S. Provisional Application No. 62/212,296, filed on Aug.31, 2015, all of which are incorporated by reference herein in theirentirety.

BACKGROUND

Non-volatile memory devices are used in electronic components thatrequire the retention of information when electrical power isunavailable. Non-volatile memory devices may include read-only-memory(ROM), programmable-read-only memory (PROM),erasable-programmable-read-only memory (EPROM), andelectrically-erasable-programmable-read-only-memory (EEPROM) devices.Some memory arrays utilize transistors and gate structures which mayinclude a charge trapping layer. The charge trapping layer may beprogrammed to store data based on voltages applied to or received by thememory array.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example, and not oflimitation, in the figures of the accompanying drawings in which:

FIG. 1 is a block diagram illustrating a computing system including anon-volatile memory system according to an embodiment.

FIG. 2 is a block diagram illustrating standby control circuitry of anon-volatile memory system, according to an embodiment.

FIG. 3A is a block diagram illustrating circuitry of a standbygenerator, according to an embodiment.

FIG. 3B is a timing diagram illustrating operation a standby generator,according to an embodiment.

FIG. 4 is a block diagram illustrating bias control circuitry, accordingto an embodiment.

FIG. 5 is a block diagram illustrating circuitry of an analog driver,according to an embodiment.

FIG. 6 is a block diagram illustrating another embodiment of standbycontrol circuitry of a non-volatile memory system, according to anembodiment.

FIG. 7 is a block diagram illustrating circuitry of voltage booster,according to an embodiment.

FIG. 8 is a flow diagram of processes of transitioning into and out of astandby mode, according to an embodiment.

DETAILED DESCRIPTION

Read operations for non-volatile memory (NVMs) devices may use analogcircuits to provide biasing for sensing circuits, to generate boostingvoltages for word-line and column drivers, as well as protectionvoltages for level shifters in a read path of the NVM device. In someimplementations, a NVM device may have an active operating condition anda standby operating condition. For example, a NVM device may enter astandby operating condition when no read or write instructions have beenreceived by the NVM device for a set length of time. The standbyoperating condition may draw less power than an active operatingcondition, however, the lower current slows the operation of circuits inthe NVM device and results in lower performance when performing readcommands.

In order to transition from a standby operating condition to an activeoperating condition, analog circuits charge various capacitors and othercircuit elements in the read path of the memory system. To avoid delaysin a high speed read operation, the analog circuits in the read path mayconsume high standby currents such that few circuit elements will becharged when transitioning into an active mode.

On the other hand, providing large standby currents in standby operationof a memory system may consume too much power for certain applications.For example, lower power system-on-chip circuits may be used inapplications having limited energy capacity to provide standby currentsand sufficient life between charging or replacing batteries. Suchapplications may include wearable devices and Internet of Thingsapplications where low power consumption extends the usefulness of theproduct or device. Devices with low power consumption may also benefitfrom fast powering up and waking up from a sleep state and fasttransition to an active state from a standby state. A transition timefrom standby mode to active mode may be substantially instantaneous andmay be similar to the propagation time of control signals in the memorysystem. For example, a fast transition from a standby state may beapproximately 1 ns or less. Such a transition may be one or more ordersof magnitudes faster than the read cycle time for the memory system (forexample, 0.01-0.1 times the length of a read cycle time). Waking from asleep state or powering up a device may be considered fast ifaccomplished on the order of microseconds (for example, 1-10 μs) becausecertain circuit elements may be charged from an inactive state. In somealternative embodiments, other lengths of time may be used to indicate afast transition from standby mode to active mode and waking from a sleepstate.

In some embodiments, control circuits operate at a low current in astandby operating condition, but provide substantially immediatetransitions from the standby operating condition to an active operatingcondition, in particular when a read instruction is received. In oneembodiment, the control circuits include a standby state detector and astart-up generator. A standby state detector may operate to determinewhen to enter or exit a standby state based on receiving read operationsat the memory system. The standby state detector may operate inconjunction with a start-up generator that provides additional powerwhen the memory system is turned on or wakes from a sleep state tocontrol the circuits generating analog signals for read operations. Thesystem may operate at low standby current when not in an active state.

FIG. 1 is a block diagram illustrating a non-volatile memory system,according to an embodiment. Computing system 100 may include aprocessing device 104 coupled to non-volatile memory system 102 viaaddress bus 106, data bus 108, and control bus 110. In some embodiments,the computing system 100 may be a programmable system on a chip (PSoC)device or similar programmable system. The components of the computingsystem 100 have been simplified for the purpose of illustration, and notintended to be a complete description. In particular, details of theprocessing device 104, address decoders 114, address drivers 116,control circuits 120, write control circuits 136, data read circuits118, and read control circuitry 124, are not described in detail herein.In some embodiments, the computing system 100 may include fewer oradditional components than illustrated in FIG. 1. For example, computingsystem 100 may include one or more additional memory components such asRAM or ROM, may include various input or output ports or devices, or mayinclude other components used by the computing system 100.

Power supply 150, is coupled to non-volatile memory system 102, alsoreferred to simply as “memory system.” Power supply 150 may be a powersupply external to memory system 102 and may be used by memory system102 to generate bias currents and voltages for providing power to amemory array 112 to read and write to the non-volatile memory. Powersupply 150 may further provide power to processing device 104 or othercomponents of the computing system 100.

Processing device 104 may reside on a common carrier substrate such as,for example, an integrated circuit (“IC”) die substrate, a multi-chipmodule substrate, or the like. Alternatively, the components ofprocessing device 104 may be one or more separate integrated circuitsand/or discrete components. In one exemplary embodiment, processingdevice 104 is the Programmable System on a Chip (PSoC®) processingdevice, developed by Cypress Semiconductor Corporation, San Jose, Calif.Alternatively, processing device 104 may be one or more other processingdevices such as a microprocessor or central processing unit, acontroller, special-purpose processor, digital signal processor (“DSP”),an application specific integrated circuit (“ASIC”), a fieldprogrammable gate array (“FPGA”), or the like.

Memory system 102 includes memory array 112, which may be organized asrows and columns of non-volatile memory cells. Memory array 112 may becoupled to address drivers 116 via multiple select lines and read lines.For example, there may be one select line and one read line for each rowof the memory array. The address drivers 116 may drive memory locationscorresponding to addresses received over address bus 106. For example,the address decoders 114 may include a row decoder, a column decoder,and a sector decoder to decode addresses received from the processingdevice 104.

Address drivers 116 may be configured to select a first row of memoryarray 112 for a program operation by applying a voltage to a firstselect line in the first row and to deselect a second row of the memoryarray by applying another voltage to a second select line in the secondrow. Address drivers 116 may be further configured to select a memorycell in the first row for programming by applying a voltage to a firstbit line in a first column, and to inhibit an unselected memory cell inthe first row from programming by applying another voltage to a secondbit line in a second column. Read control circuitry 124, in particularstandby control circuitry 126, may be configured to apply a bias currentto analog read circuits to control current provided by the addressdrivers 116 during read operations and during standby operation.

Memory array 112 may be further coupled to data read circuits 118 viamultiple bit lines. Data read circuits 118 may include columnmultiplexers and sense amplifiers. Column multiplexers may select thememory columns to be accessed by sense amplifiers during a readoperation. For example, the column multiplexers may provide access tomultiple column lines in memory array 112 to enable sense amplifiers toread multi-bit words therefrom. Memory system 102 may further includecontrol circuitry 120 to receive signals from processing device 104 andsends signals to read control circuitry 124 and write control circuitry136. The read control circuitry 124 and write control circuitry 136 maythen provide control for read and write operations of memory array 112.For example, the write control circuitry 136 may provide control of datawrite circuits 140, and the read control circuitry 124 may providecontrol of analog read circuits 128. Write control circuitry 136 mayprovide currents and voltage supplies to drivers of write path circuitsof the memory array 112. For example, the write control circuitry 136may comprise analog and digital circuits to provide high voltage to datawrite circuits 140 for writing data to memory array 112. Analog readcircuits 128 provide bias currents and voltage supplies to drivers ofread path circuits of the memory array 112, and control signals to dataread circuits 118. Read circuitry 124 includes standby control circuitry126 to generate and control standby and active operations of the memorysystem 102. The standby control circuitry 126 may provide bias currentsto word-line and column drivers, as well as protection voltages forlevel shifters in the read path of the memory circuit.

Data written to the memory array 112 or read from the memory array 112may be passed from the processing device 104 to the memory system 102through a data bus 108. The memory system 102 may include data in/outcircuits 130 that process the data passed to or from the processingdevice 104 from the memory system 102. For example, the data in/outcircuits may include one or more data buffers for controllingcommunications between the processing device and the memory array 112.

Memory system 102 may be a storage device configured to store datavalues in various low-power and non-volatile contexts. Accordingly,memory systems as disclosed herein, such as memory system 102, may beimplemented to have a relatively small area which may be fabricatedusing advanced processing nodes, such as a 65 nm node or lower.Moreover, as discussed in greater detail below, memory system 102 mayinclude various memory cells to store data values. The memory cells maybe implemented with a common source line to reduce the overall footprintof each memory cell.

Memory array 112 may include one or more memory sectors, such as sectorA 131 though sector N 132. Each sector may have any number of rows andcolumns of memory cells, for example 4096 columns and 256 rows. Rows mayinclude multiple memory cells arranged horizontally. Columns may includemultiple memory cells arranged vertically.

Memory array 112 may also use data read circuits 118 to couple a columnof memory cells in a sector to sense amplifiers during a readoperations. For example, data read circuits 118 for column 0 of sector A131 may be used as a switch to couple the memory cells of column 0 ofsector A to sense amplifiers during a read operation.

It should be appreciated that terms “rows” and “columns” of a memoryarray are used for purposes of illustration, rather than limitation. Inone embodiment, rows are conventionally arranged horizontally andcolumns are conventionally arranged vertically. In another embodiment,rows and columns of memory array 112 may be arranged in any orientation.

In one embodiment, a memory cell may be a two transistor (2T) memorycell. In a 2T memory cell, one transistor may be a memory transistor,while another transistor may be a pass transistor. In otherimplementations the memory cell may include another number oftransistors, such as a single memory transistor (1T).

Memory array 112 may be implemented using charge trapping memorytransistors. A memory array implemented using charge trapping memorytransistors may be referred to as a charge trapping memory device.Charge trapping memory transistors may be implemented to utilizetransistors and gate structures that include a charge trapping layer.The charge trapping layer may be an insulator that is used to trapcharge. The charge trapping layer may be programmed to store data basedon voltages applied to or received by the memory array 112. In this way,a memory array 112 may include various different memory cells arrangedin rows and columns, and each memory cell may be capable of storing atleast one data value (e.g., bit). Voltages may be applied to each of thememory cells to program the memory cell (e.g., program operation—store alogic “1”), erase the memory cell (e.g., erase operation—store a logic“0”), or read the memory cell (e.g., read operation).

In one embodiment, the charge trapping memory transistors may beimplemented using different materials. One example of a charge trappingmemory transistor is a silicon-oxide-nitride-oxide-silicon (SONOS) typetransistor. A memory array implemented with SONOS type transistors maybe referred to as a SONOS memory device. In a SONOS type transistor, thecharge trapping layer of the memory transistor may be a nitride layer,such as a layer of silicon nitride. Moreover, the charge trapping layermay also include other charge trapping materials such as siliconoxy-nitride, aluminum oxide, hafnium oxide, hafnium aluminum oxide,zirconium oxide, hafnium silicate, zirconium silicate, hafniumoxy-nitride, hafnium zirconium oxide, lanthanum oxide, or a high-Klayer. The charge trapping layer may be configured to reversibly trap orretain carriers or holes injected from a channel of the memorytransistor, and may have one or more electrical characteristicsreversibly changed, modified, or altered based on voltages applied tomemory cell. In another embodiment, different types of charge trappingmemory transistors may be used.

FIG. 2 is a block diagram illustrating standby control circuitry coupledto read path circuits 290, according to one embodiment. Standby controlcircuitry may include bias control circuitry 210 coupled to voltagedrivers 270 (e.g., low voltage and high voltage drivers), variablefrequency oscillator 260 to control voltage boost to read path circuits290, and one or more analog drivers 280. Standby control circuitry mayalso include a standby generator 220, a wake-up generator 230, and logicelement 235 for determining if a standby condition, wake condition, orpower-up condition is detected.

The read path circuits 290 represent various circuits used to read froma memory array. For example, the read path circuits may include dataread circuits 118 including column multiplexes and sense amplifiers, aswell as data in/out circuits 130, address decoders 114, address drivers116, or other elements of a memory system as described with reference toFIG. 1 for reading from a memory location. The additional elements shownin FIG. 2 illustrate various control and driving circuits for the readpath circuits 290. For example, voltage drivers 270, distributed analogdrivers 280, and voltage doubler 250 may be driving circuits of the readpath circuits 290, and bias control circuitry 210 may be controlcircuits for one or more of the driving circuits.

Standby generator 220, may detect if a standby condition is met in thememory system. For example, the standby generator may comprise a standbydetection circuit. The standby generator 220 may accept inputs of theclock, an enable input, and a read input. The read input may indicatewhen a read instruction is performed by the memory system. The standbygenerator 220 may determine if there has been a lapse in time since thelast read request to the memory system. For example, the standbygenerator 220 may comprise standby detection circuits for determiningwhen the memory system has entered a standby condition or when to entera standby mode. If a threshold amount of time has passed since the lastread instruction, the standby generator may produce an output indicatingthat a standby condition is met. For example, in some embodiments, thestandby generator may generate a logical high value in response todetermining that no read instruction has been received for a set numberof clock cycles (3, 4, 5, 10, or any other number of cycles, forexample). In some embodiments, a logic value of low may indicate astandby condition and a logic value of high may indicate an activecondition. Once a read instruction and an associated clock is receivedby the control circuitry, the standby generator 220 will change itsoutput to indicate that it is in an active mode. An example embodimentof a standby generator is discussed further below with respect to FIG.3.

Wake-up generator 230 may provide additional current to read pathcircuits 290 in response to waking from a sleep mode, or powering on ofthe memory system. Thus, the wake-up generator 230 may reduce the timefor initially charging the capacitors and other circuit elements in theread circuit path when the memory system is powered on or wakes from asleep mode. For example, during a sleep state, various circuit elementsof the memory system may not remain in a charged state. In order towake-up from the sleep state, an increased current may be provided bythe wake-up generator 230 to read path circuits 290. A similar processmay be performed when the memory system is powered on, as variouselements of the memory system may not be charged to operatingconditions. Thus, the wake-up generator provides increased power to theread path circuits of a memory system in response to waking up from asleep state or powering on of the memory system.

In addition to the wake-up generator, the bias control circuitry mayalso provide higher current to reduce wake-up or power-up time for thememory system. Thus, a logical output of the wake-up generator isprovided to logic element 235. The output of the wake-up generator isthus used to ensure sufficient current is provided to read path circuits290 during wake-up in addition to active modes. In some embodiments, thestandby control circuitry may not include a wake-up generator. Forexample, certain embodiments of a memory system may provide limitedpower during standby and a fast transition for the time to transition toan active mode from a standby mode, but may not have required fastpowering on or transitions from sleep mode. In such applications, astandby generator 220 may be provided in the standby control circuitrywithout the use of a wake-up generator 230. In some embodiments wherethat is the case, the standby generator is coupled to the bias controlcircuitry and may not utilize an intervening logic element 235.

Logic element 235, determines if the memory system is currently in awake-up mode, start-up mode, or active mode and if the memory system isoperating in one of these modes produces an output to the bias controlcircuitry 210, frequency divider 265, and regulator 240 (e.g. a low dropout, switching regulator, or the like) indicating that the memory systemis to operate in an active mode, which provides increased current toread path circuits 290. As shown in FIG. 2, the logic element 235 isshown as a NAND gate accepting an input from the standby generator 220and the wake-up generator 230. The input from the wake-up generator maybe inverted, such that a logic high is associated with the wake-upgenerator not operating and a logic low is associated with the wake-upgenerator in operation. Thus, the logic element 235 will produce a logiclow output if the standby generator is a logic high and the inverse ofthe output from the wake-up generator is a logic high. In otherconditions the output of the logic element 235 will be a logic high. Assuch, the logic element 235 may generate a logic low output if thestandby generator 220 indicates that the memory system is in a standbycondition and the wake-up generator is not in operation. Therefore, alogic low output of the NAND gate will indicate to the bias controlcircuitry 210, the frequency divider 265, and the voltage regulator 240to operate in standby mode and to operate in active mode if the outputof the logic element 235 is a logic high. In various embodiments, thelogic element 235 may be implemented with a different logical element.For example, the logic element may be an AND gate and a logic highoutput would indicate to the coupled circuits to operate in a standbymode. Other implementations with AND, NAND, NOR, and OR, gates may beimplemented as well. In FIG. 2, the logic output of wake-up generator230 is inverted before the circuit element 235, however, in someembodiments, the wake-up generator may produce a logic output separatefrom the driving output that is inverted. In such embodiments, theinversion prior to logic element 235 is not required. In someembodiments, the logic high and logic low of one or both of the standbygenerator and wake-up generator 230 may be reversed and a differentlogic element 235 may be used to determine if the memory system is inone of an active, wake-up, or start-up mode.

Bias control circuitry 210 provides bias currents or control signalvoltages to bring the memory system from a standby state to an activestate. For example, the bias control circuitry 210 may provide a biascurrent to variable frequency oscillator 260 to control the frequency ofoscillations provided to a voltage doubler 250. The bias controlcircuitry 210 may also provide a bitline limit voltage to one or moredistributed analog drivers 280. In some embodiments, the bias controlcircuitry 210 may also provide a protection voltage to voltage drivers270. In some embodiments, the bias control circuitry may adjust biascurrents and voltages to fewer or additional components than shown inFIG. 2. For example, in some embodiments, the bias control circuitry 210may not provide a protection voltage to voltage drivers.

The bias control circuitry may comprise multiple current mirrors forproviding bias currents in different operating conditions. For example,the bias control circuitry may provide a first set of current mirrorsthat provide standby bias currents and a second set of current mirrorsthat provide active bias currents. An example embodiment of bias controlcircuitry is illustrated in FIG. 4 and is discussed further below.

Voltage double 250 may operate to provide a boost voltage to read pathcircuits 290. For example, the power supply for the memory system mayoperate at a low voltage (e.g., 1.2 Volts), but various operations ofthe memory system may operate at a higher voltage (e.g., 2.4 Volts).Thus, a voltage doubling circuit may be provided to generate a highervoltage to read path circuits 290. In some embodiments, the boostvoltage is provided to address drivers to drive areas of the memoryarray corresponding to an address received from a processing device. Thevoltage doubler may draw significant current during active operation ofthe memory system, but may be drive read path circuits with lowercurrent during standby operation. For example, the lower current mayoperate at a level to charge a filter capacitor to maintain the voltagelevel to read path circuits 290, but not at a current to quickly drivethe read path circuits 290 as in active operation. The voltage doubler250 may receive an input voltage from a voltage regulator 240 and acontrol signal for switching from variable frequency oscillator 260 andfrequency divider 265.

The voltage doubler 250 may receive a lower oscillation frequency duringstandby operation than in active operation of the memory system. Thelower frequency results in slower switching of the circuits in thevoltage doubler 250 and therefore draws less current than operating athigher frequencies. As an example, a variable frequency oscillator 260may operate in active mode with a frequency around 50 MHz. During activeoperation, the frequency divider 165 is not active and the voltagedoubler 250 is switched according to that frequency. In standbyoperation the bias current to variable frequency oscillator 260 isreduced and a lower frequency is output. Continuing from the exampleabove, the frequency may be reduced from 50 MHz to approximately 8 MHz.The frequency may be further reduced by a frequency divider 265. Forexample, the 8 MHz output may be reduced by a factor of 8 toapproximately 1 MHz by the frequency divider. In some embodiments, thecontrol circuitry may not include a frequency divider 265, but mayoperate based only on the variable frequency oscillator 260. In someembodiments, a fixed frequency oscillator may be used, and the frequencymay be reduced only be a frequency divider 265.

Distributed analog drivers 280A-280 n operate to provide drivingvoltages and currents to read path circuits 290. In some embodiments,the read path circuits 290 may receive driving voltages and currentsfrom a single analog driver instead of multiple distribute drivers asshown in FIG. 2. The distributed analog drivers 280A-280 n may reducethe current output to the read path circuits 290 in response to biascurrents and voltage received from bias control circuitry 210. Forexample, bias control circuitry may provide a lower current the bitlinelimit voltage to the analog drivers in standby operation. Thus, thedistributed analog drivers 280A-280 n may provide enough current tomaintain charge on one or more capacitors or other elements to providefast switching to active operation from standby, but not providingadditional power to the read path circuits 290.

Similarly, the protection voltage provided to voltage drivers 270 may beprovided at a lower current to reduce power consumption by the driversfeeding the read path circuits 290. Voltage drivers 270 may operate asvoltage level shifters to shift from a low voltage control signal to ahigher voltage for driving memory cells in the memory array during aread operation. The protection voltage provided to the voltage drivers270 may prevent certain over-voltage conditions from damaging one ormore circuits in the memory system. During standby operation, theprotection voltage may be provided at a low current to maintain theprotection voltage level supplied to the voltage drivers 270. Thecurrent of the protection voltage may be increased during activeoperation of the memory system to protect the voltage drivers 270 duringpotential over-voltage events.

FIG. 3A depicts a block diagram of standby detection circuitry for astandby generator. For example, the circuitry may be implemented as astandby generator 220 as used in the example embodiment of FIG. 2. Asdiscussed above, the standby generator generates a signal to indicate astandby condition of the memory system. In some embodiments, the standbygenerator determines that the memory system is in a standby condition inresponse to a lapse in time since the previous read instruction. Thestandby generator may include two parallel paths for both rising andfalling edges of the clock signal. The standby generator may begin withan input of a read signal and a clock signal to flip flop 310. A logichigh read signal may be provided to the standby generator when thememory system is not performing a read operation. For example, when thememory system is performing write operations, the read signal may be alogic low value. When the standby generator receives a logic low readsignal, it may provide a logic low output value indicating an activecondition. This enables the circuits to operate at an active currentlevel as may be required by other operations performed by the memorysystem. For example, the oscillator may operate at an active currentlevel during write operations, so the standby generator provides anindication to operate in active mode when read operations are notperformed. A high read signal may precede an active clock signal inresponse to a read instruction to the memory system. The controlcircuitry may transition the memory system to operating in an activemode in response to pulses on the clock signal. In some embodiments theflip flop 310 may be a d-type flip flop. The flip flop 310 outputs asignal from the rising edge and the falling edge of the input signal toa series of circuit components for conditioning the signal. Inparticular, the signal passes through triggers 330A-330-B and latches340A-340B. The triggers 330 may be Schmitt triggers in some embodiments.The triggers remove noise from the signal to produce steady high and lowlogic levels. The latches 340 hold the output of the triggers for use bylogic circuits 350. The logic circuits 350 determine if the signalsindicate that the memory system is in a standby condition and produce alogic output on latch 360 that is distributed as discussed withreference to FIG. 2 above.

In some embodiments, the logic circuits 350 determine if there has beena predetermined gap since the last read instruction executed by thememory system. For example, the logic circuit may maintain the mostrecent set of signals and determine that the memory system is in anactive condition if any of the signals are logic high. In someembodiments, this may be implemented by passing the signals receivedfrom latches 340 through a series of cascaded flip flops on each clockcycle and performing a logical OR on the outputs of the flip flops. Thisoperates similar to a shift register to maintain a memory of the mostrecent signals received by the standby generator. Thus, if any of therecent values of the read input indicated logic high, the standbygenerator will output an indication that the memory system is in anactive condition, but otherwise will indicate that it is in a standbycondition. For example, to determine if there has been a read operationin the previous three clock cycles, the red signal may be input intothree cascaded flip flops. In such a configuration, the most recentsignal is on a first flip flop, the signal before is on the second flipflop, and the signal from two clock cycles ago is on the third flipflop. The output of the three flip flops may be passed to an OR gate todetermine if any of the outputs indicate a read instruction. If none ofthe flip flops indicate a logic high value representing a readinstruction, then there has not been a read instruction for three clockcycles. In such circumstances, the logic may return an indication toenter or remain in standby mode. In other situations, the logic mayreturn an indication to enter or reaming in active mode.

FIG. 3B is an example embodiment of a timing diagram of signals inputinto a standby generator and the output of the standby generator. In theexample of FIG. 3B, the “Read” input indicates that a read operation maybe performed as soon as a clock signal is present. The standby generatemay provide a “standby” output with a logic high value when the memorysystem is in a standby mode and a logic low value when the memory systemis in an active mode. At the beginning of the timing diagram, the readinput has not been active, and the standby generator is outputting alogic low value indicating that the memory system is in an activecondition. For example, the standby output may be provided as a logiclow value to enable circuits to operate in active condition for otheroperations of the memory device. At time A, the read input istransitioned from a logic low value to a logic high value indicatingthat the memory system is activated for a read instruction. Because thestandby generator has not received a clock input, the standby generatorimmediately changes the standby output to a logic high value to indicatea standby condition. At time B, the clock is activated for a readinstruction of the memory system. The standby generator immediatelychanges the standby output to a logic low value to indicate an activecondition. During the time period when the read instruction isprocessing, the clock cycles and the standby generator maintains anoutput indicating the active condition. At time C, the clock isdeactivated and no read instruction occurs, but the standby generatormaintains the active condition. At time D, the standby generatordetermines that a read has not occurred for a predetermined amount oftime and outputs a signal indicating the memory system is in a standbycondition. The standby condition is ended at time E when the clocksignal is applied to the standby generator. The standby generatorprovides a standby output with a logic low value indicating that thememory system is in an active mode.

In the example of FIG. 3B, the time between C and D may be determinedbased on the system's clock. For example, the time may be based on a setnumber of clock cycles that run indicating no read operation beforeentering a standby mode. In some embodiments, the standby generator maywait three clock cycles indicating that there has not been a readoperation before outputting a standby condition. For example, if a clockcycle is approximately 30 ns, the time between C and D on the timingdiagram may be approximately 100 ns. In some embodiments, the time maybe shorter or longer than shown in FIG. 3B. In addition, FIG. 3B is notnecessarily drawn to scale.

FIG. 4 is a block diagram of bias control circuitry as used in anembodiment. The bias control circuitry may include a standby modecurrent mirror 410, an active mode current mirror 420, a Vlim generator430 to generate a bitline limit voltage and a voltage generator 440(labeled Vprot generator) to generate a protection voltage for one ormore voltage drivers. The standby mode current mirror 410 and activemode current mirror 420 may receive an input of the standby generator'soutput. The active mode current mirror 420 may use the inverse of thestandby input to determine its operating mode.

Standby mode current mirror 410 and active mode current mirror 420 mayprovide outputs to the same circuits at different currents. For example,the current mirrors may provide a current for the bitline limit voltage(Ilim), a protection voltage (Iprot), a bias current for the variableoscillator (Ibias), and a current for reference voltages (Iref). In someembodiments, the currents from the standby mode current mirror 410 maybe significantly smaller than those generated by active mode currentmirror 420. For example, the standby currents may be 10 times or moresmaller than those of the active currents. In some embodiments, the biascurrent during active mode can be approximately 3 uA, while the biascurrents during standby mode may be approximately 300 nA. In someembodiments, the standby mode current mirror 410 or the active modecurrent mirror 420 may generate different currents for each of theoutputs. For example, the bitline limit current, the protection current,and the bias current may not be the same value.

The Vlim generator 430 and the protection voltage generator 440 generatevoltages for use in the memory system. The output of the Vlim generator430 may be a drive bias voltage and a voltage limit output as shown foruse by the distributed analog drivers. Thus, the current supplied by thecurrent mirrors determines the current of the voltages provide to theanalog drivers. The protection current generated by the Vprot generator440 may be used by the high voltage and low voltage drivers operatingthe read path circuitry of the memory system. Similar to the Vlimgenerator 430, the output of the Vprot generator 440 may be a consistentvoltage, but the current level provided at that voltage may increasebased on whether the standby mode current mirror 410 or the active modecurrent mirror 420 is operating. In some embodiments, the standby modecurrent mirror 410 operates in active operating mode and standbyoperating mode and the active mode current mirror 420 is the only usedwhen in an active condition as determined by the standby generator.

FIG. 5 is a block diagram showing the operation of distributed analogdrivers, as used in an embodiment. The distributed analog drivers may beconnected to various sectors of the memory system. For example, theremay be a driver for each sector, or each driver may be coupled to asubset of sector of the memory system. In some embodiments, there may bemore than one analog driver associated with particular memory sectors.FIG. 5 shows a PMOS controlled current source 510 and a PMOS follower520. The PMOS controlled current source 510 receives a drive bias inputand the PMOS follower 520 receives a bitline limit input voltage. Forexample, these voltages may be generated as described in FIG. 4. Theoutput voltage Vlim may be substantially constant in active and standbyoperation of the memory system. The current of Vlim, however, may behigher during an active condition of the memory system compared to thestandby condition of the memory system. For example, in standbyoperation of the memory system, the current may be adjusted such that itmaintains the charge of a filter capacitor 530. Thus, the transition toactive mode from standby mode is fast as the capacitors in the circuitare charged and increasing current provided by the bias control circuitsprovides the current to the memory system immediately.

FIG. 6 is a block diagram illustrating standby control circuitry coupledto read path circuits 290, according to one embodiment. The embodimentin FIG. 6 operates similar to that in FIG. 2, however, instead of avoltage doubler, the control circuitry uses a voltage booster 650 togenerate a boost voltage for the read path circuits 290.

FIG. 7 is a block diagram showing a voltage booster 700 as used in anembodiment. The voltage booster contains a comparator 730 thatdetermines if the supply voltage is greater than a reference voltage. Ifthe supply voltage is greater than reference voltage, the voltagebooster will provide the supply voltage to the read path circuits. Ifthe voltage supply is less than the reference voltage, the voltagebooster will provide a voltage from a change pump 720. For example, theoutput of comparator 730 as shown in FIG. 7 is provided to a multiplexerthat provides Vsupply as Vboost if the output of comparator 730indicates that Vsupply is greater than the reference voltage, andprovides the output of charge pump 720 otherwise.

The charge pump 720 may add the supply voltage to a core voltagereceived from a core voltage buffer 710. The clock to the charge pump isconnected to the core voltage. This generates the voltage of supplyvoltage plus core voltage, which is provided to a multiplexer 740 fromthe charge pump 720. The charge pump therefore generates at least aminimum sufficient voltage to supply to the memory system for properfunctioning. For example, in some embodiments, the reference voltage forcomparison is 2.5V. Thus, the multiplexer will provide the supplyvoltage if it is over 2.5V, or the supply voltage plus the core voltageif the supply voltage is less than 2.5V. In addition, the charge pumpprovides a maximum voltage of core voltage plus supply voltage. Limitingthe maximum voltage may prevent damage to memory circuits from potentialover voltage effects. Similar to the operation of the voltage doublerdescribed with reference to FIG. 2, the current used by the charge pumpduring 720 during standby mode may be reduced by lowering the frequencyprovided by the variable frequency generator and the frequency divider.In some embodiments, instead of a voltage doubler or a charge pump, thecontrol circuitry may use a pulsed voltage supply for the boost voltage,or may use a single voltage level across the memory system such that aboost voltage is not used by the circuitry.

Although generally described herein with reference to detecting astandby state of a memory system, the standby control circuitry may beused in other applications. For example, any circuit with low powerstandby requirements and fast transitioning to active mode may utilizesimilar circuits. For example, a System Resources Sub-System (SRSS)controlling operations of a system on a chip may benefit from a lowpower standby mode of control circuits during periods of inactivity, butmay start up fast when the chip is used again. For example, the start-uptime may be substantially instantaneous.

FIG. 8 is a flow diagram of processes of transitioning into and out of astandby mode, according to an embodiment. Beginning in block 810,standby control circuitry detects a standby condition of a non-volatilememory system. For example, the control circuitry may detect thecondition with the standby generator as described with reference toFIGS. 2, 3A, and 3B. Detecting a standby condition in block 810 may alsoinclude determining that the memory system is not in a wake-up conditionfrom a sleep state or a start-up condition from powering on the device.

Moving on to block 820, the standby control circuitry reduces a biascurrent to driving circuits of the non-volatile memory system. Forexample, currents may be reduced to variable oscillators, analog drivecircuits, and voltage drivers from the bias control circuitry asdescribed with reference to FIGS. 2 and 4. After the bias currents havebeen reduced, the memory system may be considered to be in a standbymode. The power consumed by the memory system is lower in standby modethan in an active mode where the memory is being accessed. When instandby mode the current to the read path circuits may be minimal andresult in maintain charging of capacitors in the read path and filtercapacitor to maintain voltage levels.

When in standby mode, the standby generator maintains an indication ofstandby mode until a read instruction is detected. In block 830, a readinstruction to the non-volatile memory system is detected. For example,the control circuitry may detect the condition with the standbygenerator as described with reference to FIGS. 2, 3A, and 3B. When theread instruction is detected, the standby generator may change theoutput to indicate to bias control circuitry to increase bias currentsand provide additional current to the read paths of the memory system.

In block 840, the current control circuitry increases the bias currentsto driving circuits of the non-volatile memory system. The bias currentsmay be increased by operating additional current mirrors to outputadditional current to driving circuits of the memory system. In someembodiments, the processes described in FIG. 8 may be performed in adifferent order. In addition, the control of current and powerconsumption by the memory system may include fewer or additionalprocesses than shown in the flow diagram of FIG. 8.

Embodiments of the present invention include various operationsdescribed herein. These operations may be performed by hardwarecomponents, software, firmware, or a combination thereof.

Although the operations of the methods herein are shown and described ina particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operation may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be in an intermittentand/or alternating manner. The terms “first,” “second,” “third,”“fourth,” etc. as used herein are meant as labels to distinguish amongdifferent elements and may not necessarily have an ordinal meaningaccording to their numerical designation.

The above description sets forth numerous specific details such asexamples of specific systems, components, methods, and so forth, inorder to provide an understanding of several embodiments of the presentinvention. It may be apparent to one skilled in the art, however, thatat least some embodiments of the present invention may be practicedwithout these specific details. In other instances, well-knowncomponents or methods are not described in detail or are presented insimple block diagram format in order to avoid unnecessarily obscuringthe present invention. Thus, the specific details set forth are merelyexemplary. Particular implementations may vary from these exemplarydetails and still be contemplated to be within the scope of the presentinvention.

What is claimed is:
 1. A method comprising: detecting a standbycondition of a non-volatile memory system; reducing bias currentsprovided to driving circuits of the non-volatile memory system inresponse to detecting the standby condition; operating the non-volatilememory system in a standby mode after the bias currents have beenreduced, wherein operating the non-volatile memory system in the standbymode comprises maintaining an output signal indicating the standby modeuntil a read instruction is detected; detecting the read instruction tothe non-volatile memory system; increasing the bias currents provided tothe driving circuits in response to detecting the read instruction; andchanging the output signal to indicate an active mode when the readinstruction is detected.
 2. The method of claim 1, wherein detecting thestandby condition comprises determining that the non-volatile memorysystem is not in a wake-up mode.
 3. The method of claim 1, whereindetecting the standby condition comprises determining that thenon-volatile memory system is not in a start-up mode.
 4. The method ofclaim 1, wherein detecting the standby condition occurs after a lapse intime since the last read request to the non-volatile memory system. 5.The method of claim 4, wherein the lapse in time corresponds to thereceipt or absence of a number of clock cycles.
 6. The method of claim5, wherein the lapse in time is at least one clock cycle.
 7. The methodof claim 1, further comprising: detecting the read instruction to thenon-volatile memory system; and increasing the bias currents provided tothe driving circuits in response to detecting the read instruction. 8.The method of claim 7, further comprising changing the output signal toindicate an active mode when the read instruction is detected.